Pulsating auroras (PsAs) are low-intensity diffuse aurora, which switch on and off with a quasiperiodic oscillation period from a few seconds to ∼10 s. They are predominantly observed after magnetic midnight, during the recovery phase of substorms and at the equatorward boundary of the auroral oval. PsAs are caused by precipitating energetic electrons, which span a wide range of energies between tens and hundreds of keV. Such energetic PsA electrons will deposit their energy at mesospheric altitudes and induce atmospheric chemical changes. To examine the effects of energetic PsA electrons on the atmosphere, we first collect electron flux and energy measurements from low-latitude spacecraft to construct a typical energy spectrum of precipitating electrons during PsA. Among the 840 PsA events identified using ground-based auroral all-sky camera (ASC) network over the Fennoscandian region, 253 events were observed by DMSP, POES, and FAST spacecraft over the common field of view of five ASCs. The combined measurements from these spacecraft enable us to obtain an energy spectrum consisting of nonrelativistic and relativistic (30 eV to 1,000 keV) electrons during PsA. The median spectrum was found to be in good agreement with earlier estimates of the PsA spectra. We then use the Sodankylä Ion-neutral Chemistry (SIC) model to assess the chemical effect of PsA electrons. The observed extreme and median spectra of PsA produce a significant depletion in the mesospheric odd oxygen concentration up to 78%.
Near-Earth space is permeated by solar plasma, driven by the slow solar winds, Coronal Mass Ejections (CMEs) or High-speed Solar wind Streams (HSSs) (Borovsky & Denton, 2006). CMEs are enormous plasma eruptions commonly caused by stressed magnetic fields around sunspots resulting in the most powerful geomagnetic storms. HSSs originate from coronal holes on the Sun. As the HSSs catch up with the slow solar wind, compression regions form, known as Co-rotating Interaction Regions (CIRs) (Richardson, 2018). Although the HSS/CIR geomagnetic disturbances typically are not as strong as CMEs, they often produce longer disturbed conditions in the near-Earth space (Zhang et al., 2007). The energetic electrons and ions from the solar wind and from the Earth's ionosphere gets trapped in the Earth's magnetosphere and forms torus-shaped regions (Shelley et al., 1972;Van Allen, 1959) constituting the radiation belts or the Van Allen belts. Investigating these trapped
Energetic electrons from the magnetosphere deposit their energy in the atmosphere and lead to production of nitric oxide (NO) in the mesosphere and lower thermosphere. We study the atmospheric NO response to a geomagnetic storm in April 2010 with WACCM (Whole Atmosphere Community Climate Model). Modeled NO is compared to observations by Solar Occultation For Ice Experiment/ Aeronomy of Ice in the Mesosphere at 72-82 ∘ S latitudes. We investigate the modeled NOs sensitivity to changes in energy and chemistry. The electron energy model input is either a parameterization of auroral electrons or a full range energy spectrum (1-750 keV) from National Oceanic and Atmospheric Administration/Polar Orbiting Environmental Satellites and European Organisation for the Exploitation of Meteorological Satellites/Meteorological Operational satellites. To study the importance of ion chemistry for the production of NO, WACCM-D, which has more complex ion chemistry, is used. Both standard WACCM and WACCM-D underestimate the storm time NO increase in the main production region (90-110 km), using both electron energy inputs. At and below 80 km, including medium-energy electrons (>30 keV) is important both for NO directly produced at this altitude region and for NO transported from other regions (indirect effect). By using WACCM-D the direct NO production is improved, while the indirect effects on NO suffer from the downward propagating deficiency above. In conclusion, both a full range energy spectrum and ion chemistry is needed throughout the mesosphere and lower thermosphere region to increase the direct and indirect contribution from electrons on NO.
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